The present invention generally relates to the depositing of small quantities of a liquid at a desired location, and more particularly, relates to a tool for dispensing extremely minute globules of liquid at a predetermined location.
Large scale, high density circuits on multilayer ceramic modules used in thermal conduction modules require engineering changes (EC) and repairs during bonding, assembly and testing. Such corrections involve the deletion of specified circuit lines and/or the rerouting of circuit lines, as is well understood in the art. The passivation of EC/repair sites is a relatively new requirement, brought about by the ever increasing number of chip input/output (I/O) terminals and the smaller chip pitches which together greatly exacerbate the crowding of the circuit components with consequent minimal clearance therebetween. Without passivation, the thermal cycling of the modules following completion of the repairs gives rise to the reflow of adjacent soldered connections and the bridging of respective components to establish unwanted circuit connections. Thus, it becomes necessary to passivate the required sites to prevent the formation of such spurious circuit pathways.
Passivation involves coating the repaired site with an insulation material which conveniently is in liquid form so that it might be applied in metered quantity and conform to the topography of the repaired site. Several approaches to the localized application of material are known in the art and variously employ hollow or solid probes carrying the material into contact with the desired location. U.S. Pat. No. 3,810,779, for example, issued on May 14, 1974, to C. G. Pickett, et al., utilizes a hollow probe which carries a droplet of liquid to a desired location on a surface. The movement of the probe is halted when the droplet contacts the surface. Deposition of liquid in the range of less than 0.3 milligrams is contemplated. U.S. Pat. No. 4,661,368, issued on Apr. 28, 1987, to Robert R. Rohde, et al., similarly employs a hollow probe but brings the probe itself into contact with the target surface in order to accurately establish a predetermined offset distance from the target surface for metered application thereto of dots of adhesive material.
U.S. Pat. No. 4,569,305, issued on Feb. 11, 1986, to Benjamino Ferri, et al., and U.S. Pat. No. 2,510,274, issued on Jun. 6, 1950, to J. F. Barry, et al., also bring a probe droplet of glue or paste into contact with a surface and the probe itself into surface contact, respectively, but utilize a solid probe, rather than the hollow probes of the aforementioned '779 and '368 patents. None of the patents cited deal with the problems associated with the delivery of metered amounts of material of such minute quantities as 2-3 mil diameter dots which correspond to a fraction of 1 nanoliter. Even micrometer-driven syringes are incapable of reproducibly delivering dots of material below about 6 mils in diameter at the present state of the art.
Passivation of repaired sites is but one application to which the present invention is directed. Passivation of repaired sites presents problems common to other applications where microdispensing of a liquid is desired. Other applications may include the microdispensing of, for example, epoxy, polyimide, fluxes, or adhesives, for various uses.